Solid oxide fuel cells (SOFCs) can be designed as high-temperature or else low-temperature fuel cells and are subdivided, depending on their type, primarily into tubular and planar solid oxide fuel cells. Planar solid oxide fuel cells are suitable, especially, for applications with high volumetric power densities. However, the reliability and service life of planar solid oxide fuel cells can be highly impaired at high pressure differences between the air side (cathode) and the surroundings, and also between the fuel side (anode) and the air side, which can be due, for example, to downstream-connected heat exchangers.
In the use of hydrocarbonaceous fuels such as, for example, natural gas, LPG, diesel or kerosene, processing of the combustion gas is necessary in order to avoid carbon deposits within the solid oxide fuel cell. Steam reforming, in addition to partial oxidation and autothermal reforming, here is the processing method having the highest potential activity. In this case, in addition to the steam which must be provided for the actual reforming of the fuel, gases such as hydrogen, carbon monoxide and carbon dioxide are advantageous in that they can generate methane via an exothermic reaction within the reformer. Since the reformate is customarily not completely oxidized in the solid oxide fuel cell, in the prior art, it is known to recirculate the gas exiting from the anode back to the reformer in a gas circuit, in order to provide the abovementioned gases hydrogen, carbon monoxide and carbon dioxide that support the processing process.
Typically, for the recirculation of the anode gas in the gas circuit, a blower or an ejector is used, through which, the recirculated material or a mixture of recirculated material and primary fuel flows.
For example, EP 1 603 181 A2 discloses a solid oxide fuel cell system in which the anode gas stream is divided before the blower.
In US 2008/0057361, an arrangement is additionally described in which the recirculation blower of the air side is situated in the recirculated material line and therefore is likewise situated downstream of the division of the anode stream into a residual gas stream and a recirculation stream.
In these SOFC system configurations known from the prior art, the pressure level of the anode, however, is set correspondingly high above the pressure drops of the downstream components of the residual gas stream. In this case, the gas pressure at the anode can reach such a high level that damage to, or failure of, the fuel cell can occur.